Here's a place where I can post my thoughts on new papers, provide updates on my projects, and post info that will eventually be on my website The Theropod Database - http://theropoddatabase.com/ . It will center on theropods, but may delve into other topics as well such as phylogenetics.

Tuesday, November 16, 2010

Ankistrodon or Epicampodon, but not Agkistrodon or Ancistrodon ...

... which was renamed Ankistrodus then Grypodon. Yay for taxonomy. Today we feature another ex-theropod taxon, from the soon-to-be-uploaded (as in, before 2011) Ex-Theropoda section of my site.

Holotype of Ankistrodon indicus (GSI coll.) in (A) lateral and (B) posterior views, with (C) a cross section of a tooth. After Huxley, 1865.

Comments- Huxley named and described the holotype, believing it to be a thecodont most similar to the parasuchian Clepsysaurus based on the presence of only distal serrations. He later (1870) referred Thecodontia to Dinosauria, leading him to refer Ankistrodon to the latter clade. Seeley (1880) mentioned the genus as a dinosaur related to Megalosaurus. He later (1885) created the genus Epicampodon for the taxon, since he incorrectly thought Ankistrodon was preoccupied by the recent viperid genus Agkistrodon Palisot de Beauvois, 1799 (or its own unjustified emmendation Ancistrodon Wagler, 1830; or the pycnodontiform fish Ancistrodon Roemer, 1849, which was renamed Ankistrodus then Grypodon). Seeley (1888) illustrated Epicampodon as an anchisaurid theropod, while Nopcsa (1901) listed it as an anchisaurine megalosaurid. It was listed as a zanclodontid theropod by Zittel (1890) and Huene (1902), who incorrectly believed it to be from the Late Triassic Maleri beds. Huene (1906) stated that the species was probably referrable to Thecodontosaurus, though he did not explicitly list the new combination until 1908. In that work he called it Thecodontosaurus(?) indicus, believing it to be most similar to Paleosaurus (his Thecodontosaurus cylindrodon). Das-Gupta (1931) thought the species was similar to his new theropod Orthogoniosaurus in having only distal serrations and having a straight distal edge (actually caused by apical breakage in indicus), placing both in Anchisauridae within Theropoda.

Huene still referred Epicampodon to Saurischia in 1940, but in 1942 recognized it was a more basal archosauriform and made it a species of Chasmatosaurus. This was followed by Tatarinov (1961), but Charig et al. (1976) correctly noted Ankistrodon has priority over Chasmatosaurus (and its senior synonym Proterosuchus). Charig and Reig (1970) and Reig (1970) considered it an indeterminate proterosuchian. Romer (1972) considered the material to be Proterosuchus without explicitly naming the new combination. Most recently, Charig et al. (1976) considered Ankistrodon a seemingly valid genus of proterosuchid, which was followed by Olshevsky (1991). While the presence of serrations does indicate an archosauriform, the Early Triassic age excludes parasuchians and theropods, and the recurved crowns exclude a relationship to sauropodomorphs like Thecodontosaurus or Anchisaurus, evidence supporting a close relationship with Proterosuchus was perhaps only given by Huene (1942), prior to the discovery of a large amount of 'proterosuchian' diversity. Recent analyses suggest that the traditional Proterosuchidae is a paraphyletic grade of basal archosauriforms, so Ankistrodon is here placed in Archosauriformes until further studies on mandibular and dental variation are performed.

Huxley (1865) also described vertebrae as belonging to Dicynodon orientalis (now Lystrosaurus murrayi), which were recognized by Huene (1942) as being archosauriform and referred to his Chasmatosaurus indicus. As the vertebrae cannot be compared to the type jaw fragment, Charig and Reig (1970) merely called them cf. Chasmatosaurus sp..

References- Huxley, 1865. On a collection of vertebrate fossils from the Panchet Rocks, Ranigunu, Bengal. Memoirs of the Geological Survey of India; Paleontologia Indica, Series IV. Indian Pretertiary Vertebrata. i, 3-24.

Huxley, 1870. Triassic Dinosauria. Nature. 1, 23-24.

Lydekker, 1880. A sketch of the history of the fossil Vertebrata of India. Journal and Proceedings of the Asiatic Society of Bengal. 69(2), 8-40.

Lydekker, 1885. The Reptilia and Amphibia of the Maleria and Denwa Groups. Memoirs of the Geological Survey of India. Palaeontologia Indica, Series IV. Indian Pretertiary Vertebrata. 1(5), 1-38.